1. Field of the Invention
The present invention relates generally to secondary cooling systems in gas turbine engines and, more particularly, to an improved arrangement defining a serial supply path for a single cooling airflow through the clearance control ring and turbine shroud of the engine.
2. Description of the Prior Art
A gas turbine engine of the turbofan type generally includes a forward fan, a middle core engine, and an aft low pressure power turbine. The core engine encompasses a compressor, a combustor and a high pressure turbine in a serial flow relationship. The compressor and high pressure turbine of the core engine are interconnected by a central shaft. The compressor is rotatably driven to compress air entering the core engine to a relatively high pressure. This high pressure air is then mixed with fuel in the combustor and ignited to form a high energy gas stream. This gas stream flows aft and passes through the high pressure turbine, rotatably driving it and the core engine shaft which, in turn, rotatably drives the compressor.
In the turbofan engine, the residual gas stream leaving the core engine high pressure turbine is expanded through a second turbine, which as mentioned above is the aft low pressure turbine. The aft low pressure turbine, in turn, drives the forward fan via a separate shaft which extends forwardly through the central shaft of the high pressure turbine rotor. Although some of the thrust is produced by the residual gas stream exiting the core engine, most of the thrust produced is generated by the forward fan.
It is common practice with respect to gas turbine engines to provide some form of cooling for the hot regions of the turbine engine. This cooling has mainly involved the use of air bled from the compressor of the engine which is then fed to the regions of the engine to be cooled. Thereafter, the air is allowed to rejoin the main gas flow of the engine.
The efficiency of a gas turbine engine is dependent upon many factors. One factor is the degree to which high pressure air generated by the compressor of the engine and intended primarily for driving the high pressure turbine after passage through the combustor is siphoned or bled off to other uses in the engine. One such use of bleed air is the cooling of the clearance control ring and shroud to achieve uniform operating clearance between the shroud and turbine blades. The greater the amount of high pressure air diverted to these other uses in the engine, the less the amount of air to drive the core turbine and thus the less efficiently the high pressure turbine will operate.
Currently, an arrangement is provided which defines separate airflow supply paths routing bleed air to the clearance control ring and the turbine shroud. This prior art arrangement requires a higher total flow of cooling air and results in a larger penalty on engine performance than is desirable. Consequently, a need exists for a more efficient arrangement for cooling the clearance control ring and shroud so as to minimize the penalty to engine performance.